The present invention relates to an arrangement in a mechanical control system of an aircraft, in which control surfaces of the aircraft can be acted upon from the cockpit of the aircraft via the control system by means of at least one control element operatively connected to the control system, for example by means of a wheel, a control column or a pair of pedals, as specified in the pre-characterising clause of claim 1.
The invention furthermore relates to a method of regulating the force which, in order to achieve a desired trim angle, must be applied to a control element for controlling an aircraft""s control surfaces, the said control element being operatively connected to a mechanical control system and comprising, for example, a wheel, a control column or a pair of pedals, as specified in the pre-characterising clause of claim 6.
Providing smaller and medium-sized aircraft with mechanical control systems in which, in manual flying, only the muscle power of the pilot acts on the control surface via cables and steering system, is already known. The aim in this case is to design the control surfaces so that the aerodynamic and mechanical forces acting on the control surfaces in flight do not become so great that it becomes difficult for the pilot to alter the control surfaces position. Some common, known solutions involve the use of various types of auxiliary control surfaces, so-called tabs, in combination with aerodynamic balancing of the control surfaces in order to achieve manageable levels of force.
With the known solutions, however, problems still remain. For example, it may be difficult to optimise the dynamic connection between torque applied and column/wheel position and it may, in particular, be difficult for a pilot to act upon the control surfaces in a critical situation, for example when the stability is suddenly lost in a roll-trimmed position and the aircraft, as a result of this, rolls strongly in either direction, which can occur as a result of heavy icing.
One object of the present invention is to produce an arrangement of the type initially referred to, which gives the pilot servo-assistance in manual flying. The object is achieved by an arrangement having the characteristics specified in claim 1.
A further object of the present invention is to produce a method of the type initially referred to, by means of which servo-assistance is obtained in manual flying. The object is achieved by a method having the characteristics specified in claim 6.
Preferred embodiments of the arrangement also have any or some of the characteristics specified in the subordinate claims.
The arrangement according to the invention has several advantages:
By means of this arrangement a linear power gradient can be obtained. A desired value can be assigned to the static power gradient. Desired values can be assigned to viscous damping and friction of the wheel. A desired magnitude can be assigned to the influence of the mass of the system on the control column/the wheel.
The positional feedback also offers the advantage that it is possible to influence the eigenfrequency of the system, so that this is not simply determined by the external load and moment of inertia of the system. Without positional feedback it is not possible to linearise any non-linear force in the basic mechanical system. Positional feedback means that a linear correlation can be obtained between the torque applied to the control column/the wheel and the trim angle.